Quick answer
Power = torque × 2π × rpm ÷ 60, and horsepower = watts ÷ 745.7. 300 lbf·ft at 5,000 rpm is 285.6 hp, or 213 kW.
Enter torque, its unit and engine speed. The calculator returns horsepower, kilowatts and metric horsepower.
Related tools: Engine Displacement Calculator: Displacement from bore, stroke and number of cylinders. Compression Ratio Calculator: Static compression ratio from bore, stroke and clearance volume. Carburetor Size Calculator: Carburetor airflow needed from displacement, peak rpm and volumetric efficiency.
How to use the Horsepower Calculator
- Enter torque (above 0).
- Choose torque unit: lbf·ft and N·m.
- Enter engine speed (rpm) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Torque | A number | > 0 |
| Torque unit | Choose one: lbf·ft; N·m | Starts at lbf·ft |
| Engine speed | A number, in rpm | > 0 |
Formula and method
Formula
P = torque × 2π × rpm ÷ 60; hp = P ÷ 745.69987
IEEE-754 double precision; shown to the decimals indicated.
Equivalent to hp = lbf·ft × rpm ÷ 5,252. 1 PS = 735.49875 W.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Torque = 300; Torque unit = lbf·ft; Engine speed = 5000.
| Result | Value |
|---|---|
| Power | 285.6 hp |
| Kilowatts | 213 |
| Metric horsepower (PS) | 289.6 |
Example 2
Inputs: Torque = 400; Torque unit = N·m; Engine speed = 6000.
| Result | Value |
|---|---|
| Power | 337 hp |
| Kilowatts | 251.3 |
| Metric horsepower (PS) | 341.7 |
Example 3
Inputs: Torque = 150; Torque unit = lbf·ft; Engine speed = 3000.
| Result | Value |
|---|---|
| Power | 85.7 hp |
| Kilowatts | 63.9 |
| Metric horsepower (PS) | 86.9 |
The first line is the headline result (power). Below it the horsepower Calculator lists kilowatts and metric horsepower (PS), which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The 5,252 rpm crossover
In US units hp = torque × rpm ÷ 5,252. Torque and horsepower curves therefore cross at 5,252 rpm: at that speed the numbers are equal. 300 × 5,000 ÷ 5,252 = 285.6 hp, matching the result.
Crank versus wheel
Engine dynamometers measure crank power; chassis dynamometers measure wheel power, which is typically 10 to 20% lower because of drivetrain losses. Make sure the torque figure and rpm are measured at the same point.
How the result changes with torque
Holding every other input at the first worked example, this table changes only torque. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Torque | Power | Kilowatts | Metric horsepower (PS) |
|---|---|---|---|
| 150 | 142.8 hp | 106.5 | 144.8 |
| 300 | 285.6 hp | 213 | 289.6 |
| 600 | 571.2 hp | 425.9 | 579.1 |
| 1200 | 1,142.4 hp | 851.9 | 1,158.2 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Torque: entering "0" shows "Torque must be greater than 0." beside that field and no result.
- Engine speed: entering "0" shows "Engine speed must be greater than 0." beside that field and no result.
Choosing between the Horsepower Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Engine Displacement Calculator](/automotive/engine-displacement-calculator/) | bore, stroke and cylinders | Displacement |
| [Compression Ratio Calculator](/automotive/compression-ratio-calculator/) | bore, stroke and clearance volume per cylinder | Compression ratio |
| [Carburetor Size Calculator](/automotive/carburetor-size-calculator/) | displacement, peak engine speed and volumetric efficiency | Required airflow |
| [Fuel Savings Calculator](/automotive/fuel-savings-calculator/) | miles driven per year, current fuel economy and new fuel economy | Annual savings |
| [Distance per Tank Calculator](/automotive/distance-per-tank-calculator/) | tank size and fuel economy | Range |
Background: vehicle sizing and speed
A taller tyre travels farther per revolution, so the speedometer reads low and the effective gear ratio becomes numerically lower; a shorter tyre does the opposite. True speed is roughly the speedometer reading times the new tyre diameter divided by the old one. Verify with GPS over a known distance before changing parts.
Assumptions and limitations
- Torque and power cross at 5,252 rpm in US units
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for torque and engine speed to confirm this.
Frequently asked questions
What is metric horsepower?
About 735.5 W, slightly smaller than a mechanical horsepower of 745.7 W.
Why do horsepower and torque cross at 5,252?
Because of the conversion constant between lbf·ft, rpm and horsepower.
Can I enter newton-metres?
Yes, choose the N·m unit.
What does the Horsepower Calculator calculate?
Power from torque and engine speed. It returns Power, Kilowatts and Metric horsepower (PS).
What formula does the Horsepower Calculator use?
P = torque × 2π × rpm ÷ 60; hp = P ÷ 745.69987. Equivalent to hp = lbf·ft × rpm ÷ 5,252.
What do I need to enter in the horsepower Calculator?
You enter Torque, Torque unit and Engine speed (rpm).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Torque and power cross at 5,252 rpm in US units.
What does the “Torque unit” option change?
It sets how the horsepower is worked out. The choices are lbf·ft and N·m.
What is an example of a horsepower result?
With torque 300, torque unit lbf·ft and engine speed 5000, the power is 285.6 hp.
Where does the method come from?
The method follows: NIST SP 811 conversions.
Related calculators
- Engine Displacement Calculator — Displacement from bore, stroke and number of cylinders.
- Compression Ratio Calculator — Static compression ratio from bore, stroke and clearance volume.
- Carburetor Size Calculator — Carburetor airflow needed from displacement, peak rpm and volumetric efficiency.
- Fuel Savings Calculator — Yearly fuel savings from a more efficient vehicle.
- Distance per Tank Calculator — Range on a full tank from tank size and fuel economy.
- EV Range Calculator — Driving range from battery capacity and energy consumption.
Sources
- NIST SP 811 conversions
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.